Evoked sensations with transcutaneous electrical stimulation with different frequencies, waveforms, and electrode configurations.

BACKGROUND: Current Perception Threshold (CPT) is a technique used for diagnostic purposes that applies sinusoidal currents transcutaneously at 5 Hz, 250 Hz, and 2KHz to preferentially excite C, Aδ, and Aß afferent nerve fibers correspondingly. This fact may be interesting for evoking different electrotactile sensations for a wide variety of applications. METHODS: Sensations evoked by 5 Hz, 250 Hz, and 2KHz frequencies; sinusoidal, square, and 250 µs-pulsed waveforms; and conventional and concentric electrode configurations were analyzed in 19 healthy volunteers. Stimuli were applied in the dorsum of the hand in a double-blind manner and CPTs were defined based on participants' verbal feedback. After each stimulus participants filled in a form with sensation modality, irradiation, intensity, and emotion descriptors. RESULTS: The frequency showed a significant effect on the four domains of evoked sensations and the waveform showed a significant effect on the modality domain. For most waveform and electrode configuration combinations, 5 Hz evoked mostly a low-intensity prickling sensation; 250 Hz mostly evoked an uncomfortable medium-intensity tingling sensation; and 2KHz mostly evoked a low-intensity tingling sensation. No thermal or noxious sensations were evoked. A significant interaction effect was only found between the frequency and the waveform factors. The electrode configuration did not show either a significant effect on the evoked sensations or an interaction effect with the frequency or waveform type. CONCLUSIONS: Transcutaneous electrical stimulation may evoke different sensations at different frequencies due to the preferential activation of different fiber types. The results of these analysis could be used to enhance human-machine/computer-interaction systems based on electrotactile feedback.

Analysis of the movements generated by a multi-field functional electrical stimulation device for upper extremity rehabilitation.

BACKGROUND: The most common chronic sequela after stroke is the loss of arm function, and functional electrical stimulation (FES) applied to the forearm muscles is one of the options to treat it. Surface multi-field electrodes have emerged, showing a great potential to improve the selectivity of the stimulation, delay muscle fatigue, and provide easier donning and doffing. The muscular selectivity takes on special relevance in the rehabilitation of the upper extremity as hand dexterity requires a wide diversity of specific muscle actions. METHODS: This pilot study analyses the movements generated in the wrist and fingers using a commercial multi-field technology-based FES device (Fesia Grasp). The study included five patients with hemiplegic subacute stroke, in which scanning of all cathodes of the electrode was carried out daily for 5 days, in two different forearm positions, with the resulting movements being labeled by experienced therapists. RESULTS: The aim of this pilot study was to determine if there were differences between subjects and between forearm positions in terms of produced movements. Movements of the wrist (two movements) and the fingers (six movements) could be achieved in two different forearm positions. CONCLUSIONS: The multi-field electrode of Fesia Grasp enables to generate a wide range of movements of the hand in different positions. This fact could allow to produce more physiological movement patterns during the rehabilitation process with FES, which could have a beneficial effect on the recovery of patients with neurological diseases.

Optimal multi-field functional electrical stimulation parameters for the "drinking task - reaching phase" and related upper limb kinematics repeatability in post stroke subjects.

BACKGROUND: No specific guidelines for the management of functional electrical stimulation (FES) parameters in post stroke patients have been defined yet, despite its frequent use. The purpose of this study is to characterize the optimal FES parameters that assist the reaching phase of drinking task ("drinking task - reaching phase") on post stroke subjects and to analyze the related upper limb (UL) movement quality indicators repeatability. METHODS: An observational study with a test and re-test design involving ten post stroke subjects with UL dysfunction was performed. End-point and joint kinematics of contralesional UL were assessed during the "drinking task - reaching phase" with FES through a test and retest design. FES parameters were adjusted to improve UL function according to a consensus between physiotherapists and patients' perspective. FINDINGS: It was possible to establish reliable FES parameters that assisted the "drinking task - reaching phase". All FES parameters presented high to very high repeatability and led to moderate to very high repeatability in almost UL movement quality indicators during the "drinking task - reaching phase". INTERPRETATION: These findings show that the main characteristics of FES parameters that improves patient perception of change are quite stable, which facilitate its implementation in clinical practice by allowing consistence between intervention sessions.

Optimal Multifield Functional Electrical Stimulation Parameters for the "Turn on the Light" Task and Related Upper Limb Kinematics Repeatability in Poststroke Subjects.

OBJECTIVE: To characterize the optimal functional electrical stimulation (FES) parameters that assist the turn on the light task (TOTL) on poststroke participants and to analyze the related upper limb (UL) kinematics repeatability. DESIGN: Cross-sectional study. SETTING: Human movement research center. PARTICIPANTS: Poststroke individuals (N=11) with history of a single unilateral stroke that resulted in a motor control dysfunction of the contralesional UL. INTERVENTIONS: FES based on surface multifield technology applied to the contralesional wrist and finger extensors during the TOTL. MAIN OUTCOME MEASURES: FES outcome metrics (virtual electrodes, stimulation duration, intensity) and kinematic metrics (end-point kinematics [absolute and relative duration, mean and peak velocities, relative instant of peak velocity, index of curvature, number of movement units] and joint kinematics [shoulder, elbow, wrist end position and range of movement]). Outcome measures were assessed 2 times with a 72-hour maximum time interval. CONCLUSION: It was possible to establish reliable FES parameters that assisted the TOTL on poststroke participants. These stimulation parameters led to high to very high repeatability in terms of UL kinematics for most of the cases.

Novel multi-pad functional electrical stimulation in stroke patients: A single-blind randomized study.

BACKGROUND: Foot drop is common gait impairment after stroke. Functional electrical stimulation (FES) of the ankle dorsiflexor muscles during the swing phase of gait can help correcting foot drop. OBJECTIVE: To evaluate efficacy of additional novel FES system to conventional therapy in facilitating motor recovery in the lower extremities and improving walking ability after stroke. METHODS: Sixteen stroke patients were randomly allocated to the FES group (FES therapy plus conventional rehabilitation program) (n = 8), and control group (conventional rehabilitation program) n = 8. FES was delivered for 30 min during gait to induce ankle plantar and dorsiflexion. MAIN OUTCOME MEASURES: gait speed using 10 Meter Walk Test (10 MWT), Fugl-Meyer Assessment (FMA), Berg Balance Scale (BBS) and modified Barthel Index (MBI). RESULTS: Results showed a significant increase in gait speed in FES group (p < 0.001), higher than the minimal detected change. The FES group showed improvement in functional independence in the activities of daily living, motor recovery and gait performance. CONCLUSIONS: The findings suggest that novel FES therapy combined with conventional rehabilitation is more effective on walking speed, mobility of the lower extremity, balance disability and activities of daily living compared to a conventional rehabilitation program only.

Temporal and Spatial Variability of Surface Motor Activation Zones in Hemiplegic Patients During Functional Electrical Stimulation Therapy Sessions.

The goal of this study was to investigate surface motor activation zones and their temporal variability using an advanced multi-pad functional electrical stimulation system. With this system motor responses are elicited through concurrent activation of electrode matrix pads collectively termed "virtual electrodes" (VEs) with appropriate stimulation parameters. We observed VEs used to produce selective wrist, finger, and thumb extension movements in 20 therapy sessions of 12 hemiplegic stroke patients. The VEs which produce these three selective movements were created manually on the ergonomic multi-pad electrode by experienced clinicians based on visual inspection of the muscle responses. Individual results indicated that changes in VE configuration were required each session for all patients and that overlap in joint movements was evident between some VEs. However, by analyzing group data, we defined the probability distribution over the electrode surface for the three VEs of interest. Furthermore, through Bayesian logic we obtained preferred stimulation zones that are in accordance with our previously reported heuristically obtained results. We have also analyzed the number of active pads and stimulation amplitudes for these three VEs. Presented results provide a basis for an automated electrode calibration algorithm built on a priori knowledge or the starting point for manual selection of stimulation points.

A decision support system for electrode shaping in multi-pad FES foot drop correction.

BACKGROUND: Functional electrical stimulation (FES) can be applied as an assistive and therapeutic aid in the rehabilitation of foot drop. Transcutaneous multi-pad electrodes can increase the selectivity of stimulation; however, shaping the stimulation electrode becomes increasingly complex with an increasing number of possible stimulation sites. We described and tested a novel decision support system (DSS) to facilitate the process of multi-pad stimulation electrode shaping. The DSS is part of a system for drop foot treatment that comprises a custom-designed multi-pad electrode, an electrical stimulator, and an inertial measurement unit. METHODS: The system was tested in ten stroke survivors (3-96 months post stroke) with foot drop over 20 daily sessions. The DSS output suggested stimulation pads and parameters based on muscle twitch responses to short stimulus trains. The DSS ranked combinations of pads and current amplitudes based on a novel measurement of the quality of the induced movement and classified them based on the movement direction (dorsiflexion, plantar flexion, eversion and inversion) of the paretic foot. The efficacy of the DSS in providing satisfactory pad-current amplitude choices for shaping the stimulation electrode was evaluated by trained clinicians. The range of paretic foot motion was used as a quality indicator for the chosen patterns. RESULTS: The results suggest that the DSS output was highly effective in creating optimized FES patterns. The position and number of pads included showed pronounced inter-patient and inter-session variability; however, zones for inducing dorsiflexion and plantar flexion within the multi-pad electrode were clearly separated. The range of motion achieved with FES was significantly greater than the corresponding active range of motion (p < 0.05) during the first three weeks of therapy. CONCLUSIONS: The proposed DSS in combination with a custom multi-pad electrode design covering the branches of peroneal and tibial nerves proved to be an effective tool for producing both the dorsiflexion and plantar flexion of a paretic foot. The results support the use of multi-pad electrode technology in combination with automatic electrode shaping algorithms for the rehabilitation of foot drop. TRIAL REGISTRATION: This study was registered at the Current Controlled Trials website with ClinicalTrials.gov ID NCT02729636 on March 29, 2016.

Neuro-fuzzy models for hand movements induced by functional electrical stimulation in able-bodied and hemiplegic subjects.

Functional Electrical Stimulation (FES) may be effective as a therapeutic treatment for improving functional reaching and grasping. Upper-limb FES models for predicting joint torques/angles from stimulation parameters can be useful to support the iterative design and development of neuroprostheses. Most such models focused on shoulder or elbow joints and were defined for fixed electrode configurations. This work proposes the use of a Recurrent Fuzzy Neural Network (RFNN) for modeling FES induced wrist, thumb, and finger movements based on surface multi-field electrodes and kinematic data from able-bodied and neurologically impaired subjects. Different combinations of structure parameters comprising fuzzy term numbers and feedback approaches were tested and analyzed in order to see their effect on the model performance for six subjects. The results showed mean success rates in the range from 60% to 99% and best success rates in the range from 78% to 100% on test data for all subjects. No common trend was found across subjects regarding structure parameters. The model showed the ability to successfully reproduce the response to FES for both able-bodied and hemiplegic subjects at least with one of the tested combinations.

Surface-distributed low-frequency asynchronous stimulation delays fatigue of stimulated muscles.

INTRODUCTION: One important reason why functional electrical stimulation (FES) has not gained widespread clinical use is the limitation imposed by rapid muscle fatigue due to non-physiological activation of the stimulated muscles. We aimed to show that asynchronous low-pulse-rate (LPR) electrical stimulation applied by multipad surface electrodes greatly postpones the occurrence of muscle fatigue compared with conventional stimulation (high pulse rate, HPR). METHODS: We compared the produced force vs. time of the forearm muscles responsible for finger flexion in 2 stimulation protocols, LPR (fL = 10 Hz) and HPR (fH = 40 Hz). RESULTS: Surface-distributed low-frequency asynchronous stimulation (sDLFAS) doubles the time interval before the onset of fatigue (104 ± 80%) compared with conventional synchronous stimulation. CONCLUSIONS: Combining the performance of multipad electrodes (increased selectivity and facilitated positioning) with sDLFAS (decreased fatigue) can improve many FES applications in both the lower and upper extremities.

Development of computer games for assessment and training in post-stroke arm telerehabilitation.

Stroke is the leading cause of long term disability among adults in industrialized nations. The majority of these disabilities include deficiencies in arm function, which can make independent living very difficult. Research shows that better results in rehabilitation are obtained when patients receive more intensive therapy. However this intensive therapy is currently too expensive to be provided by the public health system, and at home few patients perform the repetitive exercises recommended by their therapists. Computer games can provide an affordable, enjoyable, and effective way to intensify treatment, while keeping the patient as well as their therapists informed about their progress. This paper presents the study, design, implementation and user-testing of a set of computer games for at-home assessment and training of upper-limb motor impairment after stroke.

Electrical stimulation for the suppression of pathological tremor.

Pathological tremor is manifested as an involuntary oscillation of one or more body parts. Tremor greatly decreases the quality of life and often prevents the patient from performing daily activities. We hypothesized that sensors-driven multichannel electrical stimulation could stabilize affected joints by activating the antagonistic muscles during involuntary activation of agonist muscles and vice versa (out-of-phase stimulation). Here, we present the new system (hardware and software) and the testing of its operation. The hardware consists of a multichannel stimulator and inertial sensors for feedback. The software implements adaptive sensors-driven control for the out-of-phase stimulation. The system was initially applied to healthy persons at the wrist and elbow joints to test the efficiency of the hardware and software solutions. Predefined rhythmic stimulation resulted in tremulous movement, which subjects could not prevent; yet, they were still able to functionally use their hand. The system was then applied to seven patients with Parkinson's disease and essential tremor for minimization of the wrist joint tremor. In six patients, the adaptive out-of-phase stimulation resulted in a significant decrease in the amplitude of tremor (67 ± 13%). In one patient, the stimulation did not result in the expected reduction of tremor.

Wearable neural prostheses. Restoration of sensory-motor function by transcutaneous electrical stimulation.

In this article, we focus on the least invasive interface: transcutaneous ES (TES), i.e., the use of surface electrodes as an interface between the stimulator and sensory-motor systems. TES is delivered by a burst of short electrical charge pulses applied between pairs of electrodes positioned on the skin. Monophasic or charge-balanced biphasic (symmetric or asymmetric) stimulation pulses can be delivered. The latter ones have the advantage to provide contraction force while minimizing tissue damage.

The influence of electrode size on selectivity and comfort in transcutaneous electrical stimulation of the forearm.

Transcutaneous electrical stimulation (TES) is a technique to artificially activate motor nerves and muscles. It can be used for rehabilitation or the restoration of lost motor functions, e.g., in subjects with brain or spinal cord lesions. Apart from selectively activating motor nerves and muscles, TES activates sensory fibers and pain receptors, producing discomfort and pain. Clinicians try to minimize discomfort by optimizing stimulation parameters, electrode location, and electrode size. There are some studies that found optimal electrode sizes for certain stimulation sites (e.g., gastrocnemius), however the underlying effects why certain electrode sizes are preferred by patients is not well understood. We used a TES model consisting of a finite element (FE) model and a nerve model to assess the influence of different electrode sizes on the selectivity and the perceived comfort for various anatomies. Motor thresholds calculated using the TES model were compared with motor thresholds that were obtained from measurements performed on the forearm of ten human volunteers. Results of the TES model indicate that small electrodes (0.8 x 0.8 cm(2)) are more comfortable for thin fat layers (0.25 cm) and superficial nerves (0.1 cm) and larger electrodes (4.1 x 4.1 cm(2)) are more comfortable for thicker fat layers (2 cm) and deeper nerves (1.1 cm) at a constant recruitment.

Array electrode design for transcutaneous electrical stimulation: a simulation study.

Array electrodes are a promising technology that is likely to bring transcutaneous electrical stimulation (TES) a step forward. The dynamic adaptation of electrode size and position helps to simplify the use of electrical stimulation systems and to increase their clinical efficacy. However, up to now array electrodes were built by trial and error and it is unclear how, for example, the gaps between the array elements or the resistivity of the electrode-skin interface material influence the current distribution. A TES model that comprises a finite element model and a nerve model has been used to analyze the influence of array electrode gaps and gel resistivities on nerve activation. Simulation results indicate that the resistivity of the electrode-skin interface layer should be adapted depending on the size of the gaps between the array elements. Furthermore, the gap sizes should be smaller than 3mm in order to keep losses small.

Motor training of upper extremity with functional electrical stimulation in early stroke rehabilitation.

BACKGROUND: Functional electrical stimulation (FES) allows active exercises in stroke patients with upper extremity paralysis. OBJECTIVE: To investigate the effect of motor training with FES on motor recovery in acute and subacute stroke patients with severe to complete arm and/or hand paralysis. METHODS: For this pilot study, 23 acute and subacute stroke patients were randomly assigned to the intervention (n = 12) and control group (n = 11). Distributed over 4 weeks, FES training replaced 12 conventional training sessions in the intervention group. An Extended Barthel Index (EBI) subscore assessed the performance of activities of daily living (ADL). The Chedoke McMaster Stroke Assessment (CMSA) measured hand and arm function and shoulder pain. The Modified Ashworth Scale (MAS) assessed resistance to passive movement. Unblinded assessments were performed prior to and following the end of the training period. RESULTS: The EBI subscore and CMSA arm score improved significantly in both groups. The CMSA hand function improved significantly in the FES group. Resistance to passive movement of finger and wrist flexors increased significantly in the FES group. Shoulder pain did not change significantly. None of the outcome measures, however, demonstrated significant gain differences between the groups. CONCLUSIONS: We did not find clear evidence for superiority or inferiority of FES. Our findings, and those of similar trials, suggest that the number of sessions should be at least doubled to test for superiority of FES in these highly impaired patients and approximately 50 participants would have to be assigned to each therapeutic intervention to find significant differences.

A model for transcutaneous current stimulation: simulations and experiments.

Complex nerve models have been developed for describing the generation of action potentials in humans. Such nerve models have primarily been used to model implantable electrical stimulation systems, where the stimulation electrodes are close to the nerve (near-field). To address if these nerve models can also be used to model transcutaneous electrical stimulation (TES) (far-field), we have developed a TES model that comprises a volume conductor and different previously published non-linear nerve models. The volume conductor models the resistive and capacitive properties of electrodes, electrode-skin interface, skin, fat, muscle, and bone. The non-linear nerve models were used to conclude from the potential field within the volume conductor on nerve activation. A comparison of simulated and experimentally measured chronaxie values (a measure for the excitability of nerves) and muscle twitch forces on human volunteers allowed us to conclude that some of the published nerve models can be used in TES models. The presented TES model provides a first step to more extensive model implementations for TES in which e.g., multi-array electrode configurations can be tested.

New multi-channel transcutaneous electrical stimulation technology for rehabilitation.

Transcutaneous (surface) electrical stimulation (TES) is a widely applied technique for muscle atrophy treatment, muscle force training, endurance training, pain treatment, functional movement therapy, and the restoration of motor functions. We present a new TES technology based on a multi-channel stimulation approach, which allows us to perform real-time spatial and temporal variations of the electrical current density on the skin surface and in deeper tissue layers. This new approach can generate a better muscle selectivity and improved muscle activation patterns compared to state of art TES systems, which operate with predetermined electrode positions. In simulations using a finite element model (FEM) of the distal arm we could show that the nerve activation in the muscle layer is not significantly influenced by the structure of the multi-channel electrode, if the gap between elements is less than 2 mm. Experiments in healthy volunteers allowed us to measure the selectivity of single finger activations. We could also show in stroke subjects that this novel multi-channel approach was able to generate selective finger and wrist extension movements that were strong enough to overcome flexion hyperactivity. For future applications in rehabilitation a full integration of the stimulation hardware into a garment sleeve would be helpful. Once fully integrated, this new technology has a high potential to increase the ease of use, stimulation and wear comfort. It is able to improve muscle selectivity compared to state of the art TES systems, and allows the implementation of a variety of new applications for the medical and consumer market.

Overcoming abnormal joint torque patterns in paretic upper extremities using triceps stimulation.

The goal of this research project was to quantitatively assess whether transcutaneous triceps stimulation can overcome the expression of abnormal torque patterns in the paretic upper limb of subjects with hemiparetic stroke. Abnormal torque patterns consist of strong coupling between shoulder abduction (SAB) and elbow flexion (EF) or between elbow extension (EE) and shoulder adduction (SAD) torques. Both patterns reduce the active range of motion during arm movements. Eight chronic stroke subjects with moderate to severe (Fugl-Meyer assessment scores of 21/66-36/66) upper limb motor impairment participated in this study. Shoulder and elbow joint torques were measured with a 6-degrees-of-freedom load cell under isometric conditions, while the triceps muscle was stimulated to generate EE torques. At the same time the subjects were asked to lift up their arm to generate different SAB torque levels. The obtained isometric results showed that electrical stimulation can overcome abnormal torque patterns in chronic stroke subjects while generating SAB. This is likely to have potential benefits to increase the reaching workspace of the paretic arm.

Modular transcutaneous functional electrical stimulation system.

A new multipurpose programmable transcutaneous electric stimulator, Compex Motion, was developed to allow users to design various custom-made neuroprostheses, neurological assessment devices, muscle exercise systems, and experimental setups for physiological studies. Compex Motion can generate any arbitrary stimulation sequence, which can be controlled or regulated in real-time using any external sensor or laboratory equipment. Compex Motion originated from the existing Compex 2 electric stimulator, manufactured by a Swiss based company, Compex SA. The Compex Motion stimulator represents a further evolution and expansion of the ETHZ-ParaCare functional electrical stimulation system. This stimulator provides all the advanced functional electrical stimulation (FES) application and control features and can be easily incorporated into any standard rehabilitation program. Compex Motion has successfully been applied as a neuroprosthesis for walking, reaching and grasping in more than 100 stroke and spinal cord injured patients. This system has also been used to strengthen muscles and to investigate muscle properties in able-bodied subjects. Compex Motion is a multipurpose FES system specially designed to promote sharing and exchanging of stimulation protocols, sensors, and user interfaces. To the best of our knowledge an FES system that has similar capabilities does not exist yet.

Sliding mode closed-loop control of FES: controlling the shank movement.

Functional electrical stimulation (FES) enables restoration of movement in individuals with spinal cord injury. FES-based devices use electric current pulses to stimulate and excite the intact peripheral nerves. They produce muscle contractions, generate joint torques, and thus, joint movements. Since the underlying neuromuscular-skeletal system is highly nonlinear and time-varying, feedback control is necessary for accurate control of the generated movement. However, classical feedback/closed-loop control algorithms have so far failed to provide satisfactory performance and were not able to guarantee stability of the closed-loop system. Because of this, only open-loop controlled FES devices are in clinical use in spite of their limitations. The purpose of the reported research was to design a novel closed-loop FES controller that achieves good tracking performance and guarantees closed-loop stability. Such a controller was designed based on a mathematical neuromuscular-skeletal model and is founded on a sliding mode control theory. The controller was used to control shank movement and was tested in computer simulations as well as in actual experiments on healthy and spinal cord injured subjects. It demonstrated good robustness, stability, and tracking performance properties.